The earliest instruments used to monitor weather involved
the senses of the human body - especially sight, touch (feel), smell,
and hearing.
To some extent, even today these are the most important
instruments because, afterall, we study weather because we want
to know how it will impact our daily lives, and it is through
our senses that we interact with the world around us. This human
sensitivity to weather is illustrated in the attached
diagram (click the diagram to see an enlarged version of it).
Mankind and Weather

Note that as a general rule throughout this text, you may
click on any diagram to see an enlarged view of it. The new image
will appear in a new "pop-up" window. Close the pop-up window by clicking
on the "x" in the top right hand corner.

The principle parameters which we study in relation to "weather" and
"climate" are:

Once these parameters are known, other parameters such as dew point,
relative humidity, frost point and so forth may be determined as
"secondary parameters".

Despite the fact that these different phenomena affect our lives
in many ways, it turns out that the human body is not particularly
good at quantifying these characteristics. Water which feels
cold to one person may feel warm to another, depending on what that
person has been doing. For example, after a swim in an ice-cold lake,
even water at air temperature may seem warm, whereas a person
who has not been immersed in such conditions recently may consider
the same water as cool.

In addition, sometimes we are simply not very good at quantifying
things. An example is wind speed. We can get an impression of wind speed
by how severely it blows the leaves on the trees around, but that
isn't too effective in winter if there are no leaves on the trees.
One can get a crude sense of direction by watching where objects are
blown, or by holding a wetted finger up in the breeze and finding
the orientation which produces the fastest cooling. But these methods
are only approximate, and it became evident to early observers
that more quantitative measuring instruments were needed.

2. A Brief History of the Early Instruments of Meteorology

The earliest instruments were quite simple, and serious studies of the
atmosphere from a scientific perspective did not really begin until the
1800's. Before that, instruments were very simple. Examples include
thermometers,
and weathervanes.
Simple
cup anemometers
were another form of early instrument, and occasionally pressure was measured
in an approximate manner (see shortly).

Even with these tools, application was often only qualitative. For example,
weather-vanes (often with a metal replica of rooster added for
aesthetic effect (in which case they were called "weather-cocks")) were
used for little more than determining the general wind direction e.g.
whether it was blowing from
say the north or north-west. Cup anemometers gave a measure of the wind
speed, but this figure was not always quantitatively recorded.

In the 1800's, several scientists began taking more detailed measurements.
They also became curious about the atmosphere in a broad sense, including
the upper atmosphere. Examples of this type of work were the efforts
of James Glaisher (1809-1903), who became curious about what lies
"above" us, and was the first person to fly a balloon to great altitude.
In 1862 he and his pilot achieved an altitude of something in the range
29,000 to 36,000 feet (no-one quite knows for sure)
(about 9000-11,200 metres - the same
height as Mt. Everest), at which point he fainted due to the lack of
oxygen, low pressures
and cold temperatures. He measured a pressure at this height of about
one third of the ground-level pressure. His balloon pilot, although
also near unconsciousness,
was able to open a control valve with his teeth and thereby allow the
balloon to float downwards again. The attached picture shows the pilot
releasing the valve at this critical juncture.
Glaisher's pilot releases the valve.

There were several critical periods in the development of meteorology, and
the scientific application of measurement tools was one of these. Other
critical periods include the development of sophisticated computer
simulations for weather forecasting, and the advent of the space-age,
with weather satellites being placed into space.

3. Modern Instruments

In the following sections, we will describe various types of modern
meteorological tools. We will begin with the lower atmosphere, but will
also discuss instruments for measurements at heights to 100 km in altitude
at a later point. We will also briefly allude to more modern developments.

Modern instruments can be used alone, but they are most productive
when used in collaboration with other instruments. Often instruments
are placed together in a
WEATHER STATION.

Weather stations usually measure pressure, temperature, daily maximum
and minimum temperature, wind speeds, wind directions, humidity,
cloud cover, solar radiation (often at several wavelengths), and precipitation.
A good weather station must meet quite stringent requirements.
For example, they must be in an open field, so that local buildings
and obstructions do not distort their measurements of wind speed
and direction. They must be free of shade, and must meet other
important criteria. All instruments also need to be carefully
calibrated, and regularly serviced.

The following photographs show examples of the types of instruments
used (click on the small photographs to see enlargements).

Thermometers
are some of the simplest instruments, and measure
temperature.
The first thermometer was invented by Galileo in 1592.
The simplest thermometers use expansion along a tube of a liquid such as
alcohol or mercury as an indicator of temperature. There are
also adaptations of this principle which permit the thermometers
to be used to determine daily maximum and minimum temperatures.
For example, the temperature maximum can be found using a special
thermometer in which the tube holding the mercury is "pinched"
in at one point, so that Mercury may pass through it, but when the
Mercury recedes as the temperature cools, the portion above the
pinched section remains. As such it acts like a small valve, leaving
the mercury behind so that the maximum temperature can be read later.
I will not discuss these maximum- and minimum-temperature thermometers
in more detail here - there is quite a lengthy discussion on pages
75 to 77 of your text book (C.D. Ahrens, Meteorology Today, 6th ed.,
Brooks/Cole/Thomson Learning Book Co.)

However, it should be noted that not all thermometers use expansion
of a liquid in a glass column like the one shown here.
Modern devices often
are built so that the temperature can be digitized onto a computer,
and therefore use electronic means to measure the temperature. For
example, some thermometers employ the fact that the electrical
resistance of resistor elements changes as a function of temperature.
Others use the properties of thermocouples. If it is possible to
record the temperature digitally, there is of course no need to
have special devices to determine temperature maxima and minima, since
it is easy to record the data at small time steps over the whole day, and
then use software to search the data base for local maxima and minima.

As shown in the picture of the aneroid barometer, this instrument relies
on a sealed, flexible unit which contains air at a fixed volume. As the
atmospheric air pressure changes, this membrane expands and contracts,
altering the position of a needle on the barometer. Mercury barometers
use an evacuated tube, and Mercury rises or falls within this tube
as the atmospheric pressure changes, pushing the Mercury higher or lower
in the tube.

Some more sensitive instruments rely on other features related to pressure.
For example, so-called "micro-barographs" are sufficiently sensitive that
they can detect pressure changes as small as 1 Pascal or less, and these use
tiny silicon diaphragms attached to a capacitance gauge to perform
their measurements. The diaphragm bends to different degrees depending
on the external pressure, altering the capacitance of the attached
capacitor.
Data from these instruments can easily be recorded digitally, allowing
high time-resolution studies of pressure-wave events in the atmosphere.
They usually need to be carefully calibrated against more conventional
microbarographs.

Rain gauges
will be the next item we discuss. These essentially comprise
carefully calibrated collecting buckets.
The unit of rainfall that is used is equal to the depth of water
which would have
resulted on the ground if none of the water which fell could
escape (either by seepage into the ground, or by evaporation) and
if the water were spread uniformly over the whole ground.
Thus a rainfall of "15 mm" means that if all of the rain were spread
uniformly across the landscape, it would have had a depth of 15 mm.
Examples of rain gauges are shown
here.
The first one is a standard instrument, whilst the second is designed
for continuous recording. In this second case, water from the collecting
container drains onto another container which rests on a weighing scale.
The weight of the precipitation raises the arm of a recording pen,
which records the amount recorded on a paper chart.

In order to allow automation and digitization, some modern rain-gauges (called "tipping
bucket rain-gauges") tip their contents out onto a measuring scale at regular
intervals, (e.g. 1 minute) and the contents are electronically weighed
and stored digitally. The total accumulation can be determined by summing
all the weights over the course of the rain event.

Wind instruments
will be our next topic. Measurements of the wind require two parameters -
speed and direction. Direction is usually determined by a weathervane,
and there are various types of these. We have seen some earlier examples
already e.g.
, but more modern ones tend to be less aesthetic and more practical.
They also usually contain an attached instrument for measuring wind
speed as well. Examples are shown below.

Wind measuring instruments of this type usually are referred to as
wind anemometers. Because the tails of the vanes are designed
to face away from the wind, they are usually organized with a point
on the other side which points into the wind. Hence they
indicate the direction from which the wind comes.

Other forms of wind anemometers exist, such as
the one indicated
here,
which uses a fan to measure the wind speed, and contains the weather vane
as its tail.
It is also possible to obtain hand-held wind-speed anemometers like the
one shown
here.
These are not as reliable for absolute measurements, but are very portable,
and convenient for making occasional measurements at sites which do not
have a more sophisticated instrument. The observer needs to face the
instrument into the wind and record the numerical output displayed
below the fan.

Cloud height and visibility
are two other important parameters which are required for meteorological
measurements. Both use optical beams of various types - often lidars.
For example,
ceilometers
determine the base of the cloud height by sending
up pulses of light towards the cloud. Upon encountering the cloud,
the light pulses are (partially) reflected to the ground, where they
are detected.
The time delay between transmission and reception of the light pulses
is used to determine the base height of the clouds.
Visibility instruments usually measure the reduction of intensity
of narrow light beams as they traverse across a designated region.

In relation to clouds, it is also not uncommon to record the percentage
of cloud cover, and often all-sky cameras are used to do this.
A simple all-sky camera can be made by photographing the
image seen in a highly polished metal sphere with a radius of typically
15-30 cm.

Some meteorological sites also include special sensors to measure
solar radiation .
Sometimes this is done over all wavelengths, and
sometimes it is done in discrete wavelength bands. The ultra-violet
visible band is a common one to observe, due to its importance
in relation to ozone loss, but other common wavelengths include those
at which plants are most sensitive (particularly useful for
horticulture and gardening).

Humidity is another important quantity in
meteorology (both absolute and relative humidity), but in the
earlier times it proved very hard to quantify, even though human beings are
very sensitive to it. The history of the measurement of humidity
is quite fascinating, and involves some quite ingenious developments.

One of the earliest instruments for such measurements in fact drew from
human sensitivity to humidity, and in particular the sensitivity of
human hair! The attached figure shows an early example of a
Hygrometer,
This instrument uses the fact that human hair changes in length in response
to changes in humidity, with the hair becoming longer when the relative
humidity increases. Thus as the humidity changes, so the needle adjusts
in position, in response to changes in the length of the hair.

Such an instrument may seem to be a curiosity, but in fact humidity
measuring instruments which depended on human hair were common
for many years. The attached photograph shows a
Hygrothermograph.
This instrument records both humidity and temperature to a paper chart
(hence the trailing syllable "graph", rather than "meter", to indicate that
the instrument creates a graph as time evolves). It is shown with
its cover removed (the cover is at the left-hand end of the
picture). This instrument
was in use even as recently as twenty years ago, and once again depended on
human
hairs to measure humidity. The human hairs may be seen stretching from
top to bottom on the right-hand end of the instrument - in this case there
are several hairs, forming a ribbon of hair, rather than a single hair.

Another important option which may be used to measure humidity is the
Psychrometer.
The instrument shown here
has the full name of the Assmann ventilated psychrometer.
A spring-driven motor, wound up by a key at the bottom, operates a fan that
draws air across the bulbs of two thermometers. The bulb of one of the
thermometers is covered with a muslin wick, which is moistened with
distilled water. This wet-bulb thermometer is cooled by evaporation
(due to the air stream passing over it, which is generated by the fan)
to a value below the temperature shown by the dry-bulb thermometer.
The computation of the humidity is carried out by comparing the two readings
of the thermometers, since the difference between them depends on humidity and
pressure (the pressure is measured independently using a barometer).
In fact the Assmann ventilated psychrometer was actually developed
to be a portable instrument, to be flown on balloons - something
that the hygrometers could not be used for.

This Assmann ventilated psychrometer is in fact an adaptation of a much
older instrument called the "sling psychrometer", which works on the same
principle as the Assman unit. However, with the sling psychrometer the
air flow which causes the evaporation from the wet-bulb
is not generated by a fan, but rather by
whirling the unit around one's head at high speed. As with the
Assman unit, the humidity is read from a table which specifies the relation
between the temperature difference on the wet and dry bulb thermometers,
and the (relative) humidity. Such a table can be found, for example, in
Aguado and Burt, "Understanding Weather and Climate", 2nd ed., Prentice-Hall,
p. 103. A similar table can also be found in appendix D of your text book.

More recent humidity meters use a capacitor which consists of two
metal plates separated by a thin polymer film. The film absorbs or
exudes water vapour as the humidity increases or decreases, thus changing
the dielectric constant of the film. This in turn changes the capacitance
of the unit, which can be recorded electronically. The capacitance
can then be converted to a measure of humidity using suitable
conversion formulae. These instruments are very portable and
can be calibrated to quite high accuracy.

Other instruments that are used to measure the humidity include
the electrical hygrometer, the infrared hygrometer,
the dew-point hygrometer and the dew cell.
The electrical hygrometer passes an electrical current through a
carbon-coated plate, and measures the change in resistance across
the plate due to absorption or release
of water vapour as the humidity changes. The infrared hygrometer
measures the absorption of infrared light as it passes through air,
with absorption being greater when the absolute humidity is greater.
The dew-point hygrometer measures the temperature at which condensation
is produced on a cold plate, and uses this information to work
out the humidity. Finally, the dew cell actually measures the
vapour pressure of the air directly. See the text book on page 121
for further discussion of this device (last paragraph on the page).

This summarizes the main surface level instruments, although the list
is certainly not complete. We now turn to measurements above the surface.

4. Upper Atmosphere Instruments

While measurements at ground level are clearly important,
scientists have long recognized that it would be necessary to measure
at higher altitudes as well if we were ever to really understand
our atmospheric environment. We have already mentioned the
balloon flight of James Glaisher, but more sustained upper level
studies really began towards the end of the 1800's, and into the
early 1900's, with the work of R. Assmann (1845-1918) and
L. P. Teisserenc de Bort (1855-1913). These scientists developed
various instruments which could operate while being flown on kites
and balloons. An example is the Assmann ventilated psychrometer,
which we have already discussed. These scientists then developed the
art of flying their instrument collectives on kites, in aircraft
and under balloons. However, they still needed to collect
the instruments to record the data.

For a long time kites were a mainstay of meteorological measurements,
like the
box kite
shown here. They were used to carry instruments aloft, and then
could be reeled in and the equipment recovered.

Even nowadays, kites are sometimes used for special research studies.
The following picture shows a pair of kites (one red, one black) used
in some
recent experiments.
Other modern researchers have used
special kites shaped like the parachutes used in modern stunt-parachuting,
and have reached heights of several thousand metres using these devices.
The current record for the highest altitude achieved by a single kite
appears to belong to a Canadian, Mr. Richard Synergy, who reached
a height of around 4km altitude in August 2000. You can see his web site at
Richard Synergy's web site
Nevertheless, kites were eventually replaced as the main upper atmosphere
platforms, as we shall soon see.

A major advance in upper air studies
came with the development of radio techniques
which permitted the information stored on the instruments to
be transmitted back to the ground, so that even if the balloon
was lost, the user would still have a copy of the information.
Vaisala in Finland was a key player in this field, and his work
in this area led to the development of the Vaisala company,
one of the largest builders of meteorological equipment in the
world today.

Nowadays, balloons are launched from thousands of sites
around the world, carrying special packages which record
temperature, pressure and humidity. Typically these balloons
are all launched twice per day, at 0000 and 1200 Greenwich Mean
Time, although other times can certainly be used for special
experiments. Radio methods are also
used to track the balloons (either using navigation systems
or GPS techniques), so that the wind speeds at upper heights
can also be determined.

Due to the decrease of the atmospheric pressure outside of the balloon,
the balloons expand as they rise, in order to maintain pressure
equilibrium on the inner and outer surfaces of the balloon.
Eventually the balloons become so large that they burst, at
which point they fall back to earth.
Typically a balloon will reach an
altitude of 20-25 km, but specially designed balloons can
reach heights of 35 km.

These balloons carry radiosondes aloft with them. Over the years
these instruments have become smaller and lighter. They are also
relatively cheap - typically in the range of $100 to $200. Generally the
balloons fly to an upper altitude of around 20 km, where-upon they
burst, as we have already described. By the time they burst,
they have often drifted
horizontally by as much as 100 km (depending on wind conditions).
In some cases small parachutes
are attached to the radiosondes, and they float down and can occasionally
be recovered.
More often than not, however, the radiosondes are sent up without
a parachute, and the radiosonde just falls to earth and is lost.
The expense of recovering these radiosondes usually exceeds the cost
of building new ones for each flight. The sondes are usually made
with a large percentage of styrofoam, so they are light enough
that they cause no damage if they hit an object on the ground.

The radiosondes themselves have evolved considerably over the years.
Current sondes are very light-weight, and use very tiny sensors
to determine temperature, pressure and humidity. The next figure shows
a typical modern radiosonde.
Vaisala RS80 radiosonde.
The actual sensors are on a small arm which protrudes from the
cardboard casing during flight. The whole system is powered by
a water-activated battery.

The next
image
.
shows a radiosonde after it has been opened up
for examination. The main electronics are situated on a small
printed-circuit board slipped into the styrofoam casing (at the
back of the picture). The arm pointing out to the bottom holds the
sensors for determining temperature and humidity.

The next image shows a view of the
electronic circuit board
which forms the backbone of the electronics of the system,
and which acquires the data and transmits it back to the receiver at the
ground.

It was mentioned earlier that, in addition to "standard" radiosonde balloons
like the ones just shown, there are also special balloons of larger
size which can achieve greater altitudes before they burst. These often
carry ozonesondes with them, and are especially designed to measure
ozone in the stratosphere. An example is shown in the following picture.
(Click to enlarge.)
These instruments are of special importance nowadays, in view of recent
concern about loss of stratospheric ozone due to man-made (anthropogenic)
influences.

Interestingly, balloon technology has had a considerable rebirth lately.
Examples include recent attempts to build balloons which can stay
aloft for sufficient time that they can circumnavigate the world.
The first to do this were Piccard and Jones, who flew around the globe
in March 1999 in the craft
Breitling Orbiter 3.

You can read more about this in the November, 1999 issue of "Scientific
American". A great deal of modern technology was needed in order to make
a balloon which could stay aloft for sufficiently long, and there was also
a need for strong involvement from meteorologists to
direct the balloon into the
right wind conditions to ensure its continued forward motion.

Another common form of "upper air" platform is instrumented aircraft.
Aircraft can exist which can fly to great heights - even into the stratosphere-
and these are often used for special experiments. Such aircraft
have even been flown into the middle of hurricanes.

5. Rockets and Satellites

In the previous section, we implicitly treated any part of the
atmosphere above ground-level as the "upper atmosphere". In fact,
scientists have somewhat stricter nomenclature. You are aware
of the layers of the atmosphere which are defined by temperature
mean gradients i.e. the troposphere, stratosphere, mesosphere and
thermosphere. But scientists also use another classification.
The region from 10 to 100 km altitude is often called the
middle atmosphere, and the region above 100 km is then the
"upper atmosphere". For many years the "middle atmosphere" was
often referred to as the "ignorosphere", as we were ignorant
of its characteristics. However, in the years from 1980 to 2000,
many scientists (including this particular author!) have worked
vigorously to improve our understanding of this region. This has
been done especially with high altitude balloons, radars, optical
sensing and imaging techniques, lasers and lidars, rockets and satellites.
Other interesting tools have included studies of meteors, and
even studies of sound propagation. (Interestingly, the stratosphere
was first surmised because of casual observations by observers in relation
to the sounds of explosives being detonated in WWII - it turned out that
observers close to the source, and hundreds of kilometres from the
source, could often both hear the sounds, but intermediate
observers could not. This was speculated to be due to a layer
of warm air above the troposphere refracting the sound waves back down
to the ground at large distances, and this speculation eventually
proved correct. More details about these earlier types of studies
can be found in a book by A.P. Mitra entitled The Upper Atmosphere,
Asiatic Society, Calcutta, 1952. Note that in the 1950's, 60's
and early 70's, the region that we now call the "middle atmosphere"
was considered as part of the "upper atmosphere").

I will not discuss all of these techniques here. The discussion of
radar is left to another section of this course, and I have
already said something about balloons. A useful discussion about
lasers and lidars can be found at
pcl.physics.uwo.ca
and click on "General Introduction to Lidar".
(Click on the "back" arrow at the top left hand corner of the
screen to return to this page.) Passive optical
methods will not be discussed here, although they are a powerful
class of techniques in their own right, and can be used to
produce detailed images of the structure of wave events in the
middle atmosphere.
My concentration here will be on rocketry and satellites.

5(i) Rockets

Use of rockets for atmospheric studies began after world war II, when
the U.S. military began testing
V2 rockets
which had been developed in Germany as weapons of war, and which the
US had confiscated. Their tests involved flying the rockets to high
altitude, and since they would be flying through height regimes which
were previously unknown, they offered the opportunity to scientists for
them to add scientific instrumentation on board. The types of
instruments which were added were simple, and included temperature
and pressure measuring equipment, equipment for measuring cosmic rays,
and equipment for studying the ionosphere. Telemetry was also
added so that the instrument information could be transmitted
back to receivers on the ground for recording. A schematic of the
"payloads" of one of these earlier rockets is shown
here
(click to enlarge).
Such flights were the beginnings of middle atmosphere rocketry research.

After those early flights, and especially in the 1960's and 1970's,
scientists started developing their own rockets for middle atmosphere
research. These rockets were smaller than the V2's, but were especially
designed for scientific payloads. Examples of such smaller rockets are
shown in the next images, which show first a rocket on its
launch-pad,
and then a view of the rocket just after
lift-off.
(click to enlarge).

These rockets carry a variety of different payloads, and the compositions
of the payloads vary from rocket to rocket, depending on the planned
experiments. Examples include pressure sensors, density sensors,
mass spectrometers, dust detectors (for detecting meteoric dust),
ion gauges, Langmuir probes, electron density gauges, and many others.
Scientists are continually thinking of new experiments to perform, because
the middle atmosphere is a fascinating region, containing phenomena
relating to both neutral and plasma dynamics. In the section below
I will highlight just some of the many experiments performed.
It should also be noted that measurement of temperatures at these
high altitudes is not simply a matter of flying a thermometer
through the region, because the very low densities (and associated
large molecular mean free paths) and the high rocket speeds
(kilometres per second)make it difficult for slower sensors
to respond fast enough to make meaningful measurements. Special techniques
need to be employed even for a measurement as "simple" as temperature,
and past experiments have utilized experiments like measuring the
speed of sound in the different height regimes using grenade explosions as
sources, and measurements of atmospheric scale heights from pressure
and density variations with altitude.

Winds and dynamical motions form a key subject for investigation at these
high altitudes. The winds are very large and highly variable, especially
at heights of 80 to 100 km. One early method for measurement of upper
level winds was to release a trail of luminescent gas behind the rocket
as it flies upward. These particular measurements are best made at sunset
or sunrise. The trail is blown around by the wind, and also develops
a "puffy" appearance due to local turbulence, as shown
here.
By taking photographs of these trails from the ground using high
resolution cameras, and using multiple cameras so that triangulation
can be used, it is possible to determine both the upper level winds (from
the trail drifts), and the strengths of turbulence (from the rate of
expansion of the puffy trail). The numbers on the photograph
indicate height in kilometres, as determined by such triangulation.
It is also interesting to note that
at heights above about 103 km (in this case), the trail is not puffy,
but has a
more "laminar" appearance. This occurs at the higher heights
because turbulence cannot easily develop at these heights, due to
a large increase in the so-called "kinematic viscosity" of the atmosphere.
This latter term is a quantity which indicates how easy (or otherwise)
it is to stir up "eddy motions" in the air - and at the higher
heights, trying to stir up eddies is a bit like trying to
create them in honey! - the upper atmosphere is very viscous.
The transition region between turbulent and laminar motions varies
from one day to the next, but is usually fairly sharp, and somewhere
in the region between 95 and 105 km altitude. It is given the
name turbopause.

Vapour trails work best in the region between 80 and 100 km altitude.
At lower heights, other procedures are used. One example is
the inflatable
falling sphere,
(shown here being held up in the air by a person)
which is a light-weight shiny metal "skin" which is blown up with air at the
top of the rocket trajectory, and then allowed to fall to the ground.
Because it is smooth and metallic, it can be tracked by radar from the
ground, and by following the motion of this object the upper level
winds can be determined.
Other procedures include release of thousands of tiny metal
"needles", which are again blown around by the wind and can be
tracked by radar.

Many other rocket experiments are carried out, but there is currently
no real regular world-wide program of middle atmosphere rocket
measurements like the radiosonde program. Much of the information
about the long term variability of middle atmosphere winds is determined
by radars and satellites. This brings us to out next topic.

5(ii) Satellites

As rockets became more powerful, it was eventually possible to
use them to place satellites in orbit. The first successful satellite
was lifted to orbit by Russian scientists and engineers
on October 4, 1957, and was called Sputnik. Since then, many
other satellites have been placed in orbit. Currently there are
8,600 objects in Earth-orbit which have sizes in excess of 10 cm
across.

Many of these satellites exist for specific practical purposes,
like telecommunications and military surveillance, but others
are placed there for atmospheric studies. The first specialist
meteorological satellite was the
TIROS satellite,
which was placed into orbit in 1960.
Here is a view of
another Research Satellite.
These satellites have many different applications, from monitoring cloud
activity (often at several different optical wavelengths), recording
stratospheric ozone, measuring middle atmosphere temperatures, photographing
hurricanes, and measuring pollutant concentrations. Recent Canadian
satellites have been used to observe the Aurora, measure middle atmosphere
winds (WINDII, which is a special optical instrument on the
UARS satellite
), and measure pollutant concentrations (MOPITT).
Satellites offer a global coverage which is not possible with any
other single instrument, and will no doubt be major instruments in all
future work, but they are usually far more efficient if used in parallel
with ground-based instruments like radar and radiosondes. The future
of atmospheric research will undoubtedly involve all of the many
instruments which I have discussed.